1. Field of the Invention
The present invention relates to an organic light emitting diode display, and more particularly to an organic light emitting diode display that is adaptive for effectively emitting a heat which is generated at an organic light emitting diode device.
2. Description of the Related Art
Recently, various flat panel display devices have been developed to reduce the weight and bulk so as to replace a relatively heavy and large-bulk cathode ray tube. Such flat panel display devices include a liquid crystal display (hereinafter, referred to as “LCD”), a field emission display (hereinafter, referred to as “FED”), a plasma display panel (hereinafter, referred to as “PDP”), and a light emitting diode display, etc.
The PDP has a relatively simple structure and manufacturing process. Therefore, the PDP is most advantages to be made large-sized, but it has a disadvantage of a low luminous efficiency, a low brightness, and high power consumption. Since the manufacturing process for the LCD is similar to the semiconductor process, the LCD is difficult to be made large-sized screen, and the LCD has a disadvantage in that power consumption is increased by a backlight unit. Furthermore, the LCD has a disadvantage in that its viewing angle is narrow and there is a high light loss by optical devices such as a polarizing filter, a prism sheet, and a diffusion plate, etc. On the other hand, the light emitting diode display has an advantage of a fast response speed, a high luminous efficiency, a high brightness, and a wide viewing angle.
The light emitting diode displays are largely classified into an inorganic light emitting diode display and an organic light emitting diode display depending upon the used material.
The OLED is driven with a low voltage of about 5V to 20V compared to the inorganic light emitting diode display which requires a high voltage of about 100V to 200V. Thus it possible to drive the OLED with a DC low voltage. Furthermore, since the OLED has an excellent characteristic such as a wide viewing angle, a fast response speed, and a high contrast ratio, etc., the OLED can be used as a pixel of a graphic display, a pixel of a TV picture display, or a pixel of a surface light source. Moreover, since the OLED has an advantage of thin and light weight, good color impression, it is a suitable device for the next generation flat panel display.
A method of driving the OLED is largely classified into an OLED of passive matrix type and an OLED of active matrix type.
The OLED of passive matrix type has a simple structure and a simple manufacturing process. However, the OLED of passive matrix type has a disadvantage of high power consumption. Furthermore, it is difficult to be made a large-sized. Moreover, the OLED of passive matrix type has a disadvantage in that an aperture ratio is deteriorated as the number of wire lines increases.
On the other hand, the OLED of active matrix type has an advantage of a high luminous efficiency, a high picture quality realization.
Moreover, the OLED is largely classified into a top emission type and a bottom emission type depending upon a light emitting direction thereof.
FIG. 1 is a diagram showing a bottom emission type OLED of the related art.
Referring to FIG. 1, the bottom emission type OLED of the related art includes an organic light emitting diode device 4 and a cap 6. Herein, the organic light emitting diode device 4 is formed at a front surface of a transparent substrate 2. The cap 6 packages the organic light emitting diode device 4.
The organic light emitting diode device 4 includes a first and second electrodes and an organic light emitting layer. The organic light emitting layer includes an electron injection layer, an electron transport layer, a light emitting layer, a hole injection layer, and a hole transport layer. If a voltage is applied between the first electrode and the second electrode, an electron and a hole which are generated from the first electrode and the second electrode move toward a light emitting layer via the electron injection layer, the electron transport layer, the hole injection layer, and the hole injection layer, respectively: Thus, the electron and the hole are re-combined to generate a light in the organic light emitting layer. As a result, the light is emitted to the outside via the transparent substrate 2 so that a picture is displayed.
The organic light emitting diode device 4 has characteristic which is easily degradated by a gas and moisture. To solve this problem, the organic light emitting diode device 4 is protected from an external gas and moisture by an encapsulation process. Herein, the encapsulation means that the transparent substrate 2 and the cap 6 provided with the organic light emitting diode device 4 are bonded with each other by a sealant 10 such as an epoxy resin, etc. In this case, the cap 6 is mainly formed of a glass, and a getter 8 is formed at the cap 6. Herein, the getter 8 is located on a surface which opposes to the organic light emitting diode device 4 to absorb a gas and moisture.
A light and a heat are generated at the organic light emitting diode device 4 in the case where the OLED is driven. Actually, a temperature of about 50° C. is measured at the outside upon 300 nit light-emitting in the case where an OLED of 2.2 inch is driven. The generated heat degradates the organic light emitting diode device 4, thus causes a deterioration of the span of life. Since a glass which is used at the cap 6 has low heat conductivity, a heat which is generated at the organic light emitting diode device 4 within the cap 6 is not effectively emitted.